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Abstract

In this thesis, I describe large-scale and small-scale features of the Antarctic Circumpolar Current (ACC) by merging conductivity-temperature-depth (CTD) data
obtained by novel animal-borne sensors with data obtained by more conventional
means. Twenty-one CTD-Satellite Relay Data Loggers (CTD-SRDLs) were attached
to Southern elephant seals (Mirounga leonina) on South Georgia in 2004 and 2005.
This was part of a larger international study (Southern Elephant Seals as Oceanographic Samplers; SEaOS), in which I played a major role in developing the oceanographic approach used to integrate physical data from a range of sources, and the means to link biological findings to oceanographic parameters.
The development of animal-borne oceanographic sensors and their potential place within an ocean observing system is reviewed initially. Then, I describe the Series 9000 CTD-SRDL in detail, discussing its performance in the lab and during two field experiences with Southern elephant seals and Weddell seals (Leptonychotes weddellii ).
Following this, a detailed study of the ACC frontal system in the South Atlantic is
presented that uses merged Argo float data and CTD-SRDL data. The structure of
the frontal field revealed by this unique dataset is examined, and unprecedented insight into its variability is obtained. Amongst the important findings is that, contrary to most climate models, our in situ data suggest a northward shift of the ACC east of 40W in 2004 and 2005 compared to previous work. Next, two CTD-SRDL sections
are presented to identify the locations of the ACC fronts across Drake Passage,
and an empirical relationship between upper ocean temperature and baroclinic mass
transport is used to determine the transport through Drake Passage at the times of
the sections. This technique is a powerful complement to more conventional means
of data collection in this region, especially given the ability of the seals to conduct "sections" at times when ship-based fieldwork is logistically most challenging, i.e. in the winter time.
The CTD-SRDLs do not only record hydrographic data, but simultaneously record
seal movements and diving behavior. This enables insight to be obtained on the behavioral and physiological responses of Southern elephant seals to spatial environmental variability throughout their circumpolar range. The resulting energetic consequences of these variations could help explain recently observed spatially varying population trends. With a stable population at South Georgia and declining populations at
Kerguelen and Macquarie Island. This study also highlights the benefits to the sensorcarrying animals themselves by showing the usefulness of this approach in examining
the sensitivity of top predators to global and regional-scale climate variability. More
importantly, I conclude that, by implementing animal-borne sensors into ocean observing strategies, we not only gain information about global ocean circulation and enhance our understanding of climate and the corresponding heat and salt transports,
but at the same time we increase our knowledge about ocean’s top predators, their
life history and their sensitivity to climate change.